\begin{tikzpicture} [every node/.style={anchor=south,,inner sep=0}]
	\node (y) {约定:};
    \node [right = 1em of y] (1) {$off_{1} = 0$,};
    \node at ([xshift=4.5em,yshift=-1.5em]1.south) (2) {$off_2=off_1 + \text{LEN}(tp_1)$, \dots\dots};
    \node at ([xshift=-0.25em,yshift=-1.5em]2.south) (3) {$off_n = off_{n-1} + \text{LEN}(tp_{n-1})$};
\end{tikzpicture}